1. Field of the Invention
The invention relates to ion analyzers and, more specifically, to a combined ion measurement/calibration cell.
2. Background Information
A variety of industrial and other fields commonly rely on the measurement of ions in solution for such applications such as controlling industrial processes, assessing water quality, and the like. A particularly useful ion measurement and calibration cell is described in U.S. Pat. No. 4,600,494, issued Jul. 15, 1986 to Edward Bromberg et al. The teachings of this patent are incorporated herein by reference.
The '494 patent describes an ion analyzer cell having two modes of operation, the first a measurement mode in which the concentration of an ion in solution is measured, and the second a calibration mode in which the ion concentration in a carefully prepared and controlled sample is measured in order to calibrate the cell. The measurements are performed with a pair of potentiometric electrodes mounted in the cell. A first electrode of the pair serves as a measuring electrode; a second electrode of the pair serves as a reference electrode. The electrodes are separated by a partial baffle which largely, but not completely, isolates them from each other.
The baffle allows limited fluid communication between the electrodes to thereby provide the required electrical continuity for potentiometric measurement, while largely isolating their immediate environments to minimize contamination of the measuring electrode by seepage from the reference electrode. Even with such a baffle, however, there is still some flow (“backflow”) of electrolyte from the reference electrode to the measuring electrode. When very small ion concentrations are being measured, this backflow can interfere with the ion measurement and degrade its accuracy.
Ion measurements are frequently made in industrial environments by users with little experience in, or knowledge of, precise chemical processes. For such users, it is important to provide as much assistance as possible in the use of the measuring apparatus, without unduly complicating the system. Printed manuals are often quickly lost or rendered illegible by spills and other abuses. Electronic displays are frequently too expensive or too limited to provide the required assistance.